Forensic Science Review

Set of flashcards related to forensic science

Unreliable Eyewitness Accounts

Misremember what they saw, and imagine some things happened when they actually didn’t.

Photo Array Procedures

Administrators should be uninvolved in case; photos should have similar layouts and subject traits

Testimonial vs. Physical Evidence

Testimonial evidence is evidence that is provided by a witness: whereas physical evidence are items that may be actually found at the crime scene. Physical evidence is generally more reliable .

Trace vs. Transient Evidence

Trace evidence would be the small evidence that can be found at a crime (e.g., bullets) whereas transient evidence is evidence that can degrade/disappear quickly.

Class vs. Individual Evidence

Class evidence is evidence that can generally be tied back to any person, whereas individual evidence is mainly to one person, class evidence can be increased when we use DNA sampling.

Locard Exchange Principle

Someone will bring something to the crime and leave with something from it, therefore making them a more identifiable suspect.

Steps to Processing a Crime Scene

1) secure the scene 2) separate the witnesses 3) scan the scene 4) see that photos are taken 5) sketch the scene 6) search for evidence 7) secure collected evidence

Crime Scene Sketch Inclusions

Rough outline, measurement of room, furniture and items, direction arrow

Patterns for Searching a Scene

Spiral, grid, strip/lane

Collection Methods for Evidence

Liquid: airtight, unbreakable containers; Wet items (biological): dry out in breathable container; Dry item: bindle, plastic or paper container, seal w/ tape and labeled with pertinent info.

Layers of the Skin

Inner layer: dermis; Outer layer: epidermis; Basal layer is in between

3 Fingerprint Principles

1) Fingerprint is an individual characteristic; no two people can have the exact same fingerprint 2) Fingerprint pattern will remain unchanged for the life of an individual; unless scarred or skin disease 3) Fingerprints have general characteristic ridge patterns that allow them to be systematically identified

Types of Prints at a Crime Scene

Patent- visible prints seen without magnification (from blood, ink, etc); Latent- hidden or invisible by dusting with powder/ chemicals; Plastic- indentations left in clay/ wax

Layers of Hair Structure

Cuticle- outside, scales overlap; Cortex- inner layer, has pigment; Medulla- inner most layer

Human vs. Animal Hair

Human- imbricate; Animals- spinous/ coronal

Hair as Class vs. Individual Evidence

Class evidence unless a root and follicle is present

Ways Forensic Scientists Analyze Fibers

Microscopic observations, Burning, Chemical tests, Thermal decomposition, Density, Refractive index, Fluorescence, chromatography

Fiber connection to crime scene

Fibers are transferred from person to person, and place to place, indicating where someone has been

Blood types and the blood they can receive from.

A: A, O; B: B, O; AB: A, B, AB, O; O: O

Types of spatter patterns.

Wipes- object moving through partially dried blood with lateral motion, altering appearance, patterns created when a target moves through an existing wet blood stain on another object, Swipes- lateral transfer of wet blood from a moving source onto a surface, Transfer Stains- when a wet, bloody object comes in contact with a target surface, Arterial Spurts- caused by blood exiting an artery, Cast off spatter- a bloodstain pattern that is created when a blood-bearing object is in motion and emits blood

The structure of DNA

Double Helix: Two coiled DNA Strands Composed of nucleotides that contain: A Sugar molecule, Phosphate group, Nitrogen-containing base

Different types of DNA

Nuclear- found in the nucleus; Mitochondrial- found in the cytoplasm

How do PCR and gel electrophoresis work

PCR: 1) Heat the DNA strands, cause them to separate 2) Cool the mixture and add a primer, a.k.a base pairs that’ll add sequence onto DNA Strand 3) Add a DNA polymerase and a mixture of free nucleotides to the separated strand; Gel electrophoresis: 1) Separates DNA fragments by length 2) Longer strands move through the gel more slowly 3) The smaller, lighter molecules will move the furthest on the gel

Function of restriction enzymes.

Recognize a specific sequence of nucleotides in double stranded DNA, and cut the DNA at a specific location

What does a forensic pathologist do?

Performs autopsies, determines time/manner of death

The progression of rigor mortis, liver mortis, algor mortis, and decomposition.

Algor mortis → using body temperature to determine T.O.D, a body loses 1.5 degrees F per hour. So: 98.6-bodytemp/1.5= number of hours deceased ; Rigor Mortis → muscle tissue shortens, body stiffens. Begins after 12 hours, ends after 48; Livor Mortis → Begins 2 hours after death, permanent after 8

Desiccation

body dries out/loses moisture

Forensic entomologist.

Applies knowledge of insects to provide info for criminal investigations

PMI based on insects.

Based on how long it’s been after death, specific species of insects may appear in various larvae stages

life stages of commonly found flies.

Blow Fly: 1st: adult flys lay eggs 2: eggs hatch into larva (maggots) in 12-24 hours 3rd: larvae continue to grow and molt (shed exoskeletons) as they pass through various instar stages 4: the larvae develop into pupa after burrowing in soil 5. Adult flies emerge from pupa cases after 6-8 days

Correlate the stages of decay with the presence of different types of insects

Early stage decomposition: carrion beetles, Early to late stage decomposition: rove beetles, clown beetles, Late stage: ham & checkered beetles, skin beetles, hide beetles

How do we scale down to fit piece of paper?

Identify the room's longest measurement. Divide this real-world measurement by the largest dimension of your usable drawing paper (in the same unit). Round this factor up to a convenient whole number or simple fraction. This becomes the second number in your ratio scale (the first is always 1). EX:: 1) A room is 35 feet long, and your usable paper length is 8 inches (allowing for margins). 2) 35 feet * 12 inches/foot = 420 inches (note- we have to convert to INCHES because that’s the unit we are measuring our paper in). 3) 420 inches / 8 inches ≈ 52.5. 4) Rounding up to 60 gives a scale of 1:60. 5) To create a unit scale, 60 inches = 5 feet, so the scale is 1 inch = 5 feet.

Why do humans have fricton ridges?

To help grip objects

How are fingerprints formed?

Fetal development when skin folds and crease

What are some minutiae patterns?

Crossover, scar, core, bifurcation, ridge ending, island, delta, pore

Techniques of collecting prints/ when to use

- Black powder and clear tape - Fluorescent light on dark/ multicolored surfaces - Cyanoacrylate method- super glue method, used to develop latent prints on a variety of objects - ninhydrin - chemical that bond amino acids to prints to produce blue/purple color ( surfaces like paper or cardboard)

What are possible medula patterns?

Fragmentary - Interrupted - Continuous - Stacked (animal)

Know the possible cuticle patterns

Uniserial - Multiserial - Vacuolated - Lattice - amorphous

Know the 6 things that can be determined from hair evidence

- Origin (animal or human) - Body area - Hair color - Whether hair was forcibly removed - Potential presence of drugs/ toxins ● If hair was chemically treated

Is fiber class or individual evidence

Class

How does a burn test work?

Observing flame color, smoke produced, smell, residue

What types of chemical tests might you use?

Solubility, burning, staining

How are fibers collected at a crime scene?

Paper bags- clothing, dry clothes if needed Tape lifts- collecting bits of evidence on tape Folded into paper- small fibers

How do artificial and natural fibers differ?

Artificial- thousands of fibers, treated chemically Natural- limited number of fibers

What are 8 blood types?

A+ : Contains Anti-A and Anti-D A- : Contains only Anti-A B+ : Contains Anti-A and Anti-D B- : Contains only Anti-B AB+ : Contains Anti-A, Anti-B, and Anti-D AB- : Contains Anti-B O+ : Contains Anti-D O-: Doesn’t contain antibodies

How do we determine blood type? How does that process work?

Through mixing the blood with different antibodies and look for agulation

● How do you measure a blood droplet?

Measure the width and length of the blood droplet

● Identify point of origin of blood spatter and area of convergence

Point of Origin: PO=tan(Aol)*y Area of convergence: drawing straight lines through blood drops to connect and find area of convergence

● Calculate angle of impact

Sin^-1(width/length)

● Determine relative velocity of impact (low, medium, high)

High- caused by a gun or high speed machinery, fine mist-like droplets Medium- caused by beating, moderate-sized droplets Low- caused by a blunt object or dripping, larger drops

What are two types of DNA? Where are they found?

Nuclear- found in the nucleus Mitochondrial- found in the cytoplasm

Which type of DNA is used for identification purposes?

Nuclear DNA, because mitochondrial DNA is more rigorous/time-consuming

How can DNA techniques be used to match DNA samples?

• PCR: can amplify specific sequences of DNA • Gel: Separates and visualizes based on size, can allow us to analyze genetic material

Understand the difference between a coroner and a medical examiner/forensic pathologist

Corner: typically elected, may not always be a medical professional Forensic pathology: usually is always a physician with some type of medical background

What does a forensic pathologist do?

Performs autopsies, determines time/manner of death

Distinguish between cause mechanism and manner of deatj

Cause: the specific, medical reason someone died Manner: the legal classification, can be natural, accident, suicide, or homicide Mechanism: The event that actually causes the death, (blood loss, respiratory problems)

Order of autopsy operations

1. Measurements of outside surface 2. Inspection of external surface ● Y Incision ● Open Rib Cage ● Condition of heart ● Remove organs

Be able to use the above to approximate time of death (including the formula for algor mortis)

98.6-bodytemp/1.5= number of hours deceased

Understand the impact of environmental conditions on the above

Temperature: the colder, the faster, the warmer, the slower Wind: the windier, the faster, the calmer, the slower

Be able to use stomach contents and the progression of digestion to approximate PMI

If there’s undigested food, death occurred 0-2 hours after meal Digested food in small intestine not stomach means death occured 4-6 hours after meal Food in large intestine but not small or stomach, death occurred 12+ hours after

Be able to use clouding of the cornea to approximate PMI

Open: , 2 hours Closed: 24 hours

What a forensic entomologist does

Applies knowledge of insects to provide info for criminal investigations

● How insects can be used to determine PMI

Based on how long it’s been after death, specific species of insects may appear in various larvae stages

What types of insects are most likely to be found

Flies and beetles

● The life stages of commonly found flies

Blow Fly: 1st: adult flys lay eggs 2: eggs hatch into larva (maggots) in 12-24 hours 3rd: larvae continue to grow and molt (shed exoskeletons) as they pass through various instar stages 4: the larvae develop into pupa after burrowing in soil 5. Adult flies emerge from pupa cases after 6-8 days

Be able to use the life stages of various insects to approximate PMI (note- you do NOT need to memorize the time intervals of each stage, but given the time intervals, you should be able to estimate TOD)

Flies: first 3 months Dermestid beetles: 3-6 months Various flies and beetles 4-8 months Dermestid beetles: 1-3 years

● Correlate the stages of decay with the presence of different types of insect

Early stage decomposition: carrion beetles Early to late stage decomposition: rove beetles, clown beetles Late stage: ham & checkered beetles, skin beetles, hide beetles

● Understand the impact of environmental conditions and the presence of drugs in the blood on insect development

The presence of drugs might impact larvae development and the environmental conditions may lead to the appearance of some species but not others